Explain battery voltage?

[BigBlue1]

I'm not really looking for where the leakage is, my disconnect switch will fix that, and provide a key-less security feature. I'm just wondering why the voltage around "the loop" doesn't match (add up). (It HAS to. Kirchoff's Voltage Law)

I would expect that the resistance of the meter would be high enough so that no current flowed through the meter when I measured the voltage between the battery neg (-) post and the neg (-) cable, with the cable disconnected. I would expect this voltage to be 12.6V. Exactly the same as across the battery posts (12.6V).
But I only measure 11.7V.
So where did the other .9V go?

I wouldn't expect a Voltage Meter to pass that much current through itself. However, if the meter's resistance is low, enough current must flow through it when measuring voltage, that I get a voltage drop (0.9V) across the ATV components from this current. It's the only thing that makes sense, because there doesn't seem to be any other path. This is surprising.

The other 0.9V went into dropping across the resistance of everything else in the circuit between the two voltmeter probes. From the negative battery terminal to the battery plates to the positive terminal to the positive cable to everything else in the closed circuit to the vehicle's ground/frame to the negative cable to the negative cable clamp. All those inches of wire (small resistance) and all the minor resistance at each connection drops the voltage some.

For a simplistic example that demonstrates, go get a 100' extension cable, fashion connection with one of the leads to your (+) battery post and then measure between the (-) battery post and the other end of the extension cord. It won't be the same as the voltage between (+) and (-) posts. Now plug in a couple smaller ext cords and watch voltage drop further, from additional length and each imperfect connection. Same concept applies to your vehicle test.

Rob

 

[MossRoad]

I measured the voltage between the battery neg (-) post and the neg (-) cable, with the cable disconnected.

You still have the resistance of every piece of wire, connector, electrical components, etc... in the circuit from the positive post, down the wire, into the starter, into any other components, through the frame, and back up the negative wire.

All of those components have resistance and drop the voltage.

 

[TCJatko]

Have you checked the connection to the frame or other ground point on the battery negative cable? Sounds like you have a poor connection there.

 

[CobyRupert]

You still have the resistance of every piece of wire, connector, electrical components, etc... in the circuit from the positive post, down the wire, into the starter, into any other components, through the frame, and back up the negative wire.

All of those components have resistance and drop the voltage.

Yes, but remember that you should only get that voltage drop when there is current flowing. (Remember, the neg (-) cable is disconnected from the battery post, so there's no path for current to flow)

I would of never guessed that the mere act of measuring voltage with a voltmeter across this open connection (between battery and cable) would allow enough current to flow through the meter that I get such a significant voltage drop through the paths on the ATV. (i.e. I would of never believed that two (2) different Voltmeter's internal resistances are low enough to allow so much current through)

 

[Industrial Toys]

The resistance of a meter, particularly a digital one is VERY high. Like millions of ohms. If not, you would put a load or even a short on the circuit being measured. I seem to recall that old cheaper analog meters might have had 10 or 100, 000 ohms resistance. The more expensive meters had higher reistance and the really expensive one, higher still with transistor amplifiers.

 

[MossRoad]

OK I got ya. You're thinking your meter is letting current through?

 

[WranglerX]

The voltage drop is not important, what is important is the drain....

If you are seeing a drain with everything shut off the means you still have a loop circuit, which you should not (except if you have ECM) if you don't find device that is causing current loop you are not going to solve the running down of battery...

Keep disconnecting things till what is causing the drain is found....Fix that item...

Easiest fix may just put a battery disconnect in either cable and at end of work session just "disconnect"....

Battery Switches

Probably find one down the street at FLAPS...

Dale

 

[CobyRupert]

The resistance of a meter, particularly a digital one is VERY high. Like millions of ohms. If not, you would put a load or even a short on the circuit being measured. I seem to recall that old cheaper analog meters might have had 10 or 100, 000 ohms resistance. The more expensive meters had higher reistance and the really expensive one, higher still with transistor amplifiers.

Exactly! This is why it doesn't make sense.

OK I got ya. You're thinking your meter is letting current through?

...or maybe I've stumbled upon a tear in the space-time continuum where Kirchoff's Voltage Laws doesn't apply and I can somehow capture this unexplained/mystery 0.9 Volts to power a perpetual motion machine.

Yes, I've put a disconnect switch on the cables, but when it's open: I still get 12.6 volts across battery terminals, and 11.7 volts across the open switch!
Kirchoff, where are you!!

 

[RandyT]

ECU as well as a voltage regulator if battery voltage is not disconnected by the key in the off position all the time. This is normal and anything under 100 milliamp is considered normal when measuring between the negative post of the battery and the disconnected negative battery cable with an amp meter.

 

[Ford850]

Exactly! This is why it doesn't make sense.



...or maybe I've stumbled upon a tear in the space-time continuum where Kirchoff's Voltage Laws doesn't apply and I can somehow capture this unexplained/mystery 0.9 Volts to power a perpetual motion machine.

Yes, I've put a disconnect switch on the cables, but when it's open: I still get 12.6 volts across battery terminals, and 11.7 volts across the open switch!
Kirchoff, where are you!!

But you are bridging that open circuit with the meter. Similar to you bridging the open circuit between the posts with the meter.